Electric fuse having stress-reducing fuse link means



July 23, 1968 c, JACOBS, JR 3,394,333

ELECTRIC FUSE HAVING STRESS-REDUCING FUSE LINK MEANS Filed Aug. 24, 1967 2 Sheets-Sheet 1 F IG.4 1 g; 511

INVENTOR. PHILIP C. JACOBS JR.

BY M RAM/ m P. C. JACOBS, JR

ELECTRIC FUSE HAVING STRESS'REDUCING FUSE LINK MEANS 2 Sheets-Sheet 2 July 23, 1968 Filed Aug. 24, 1967 am l i 7 1 INVENTOR= United States Patent ABSTRACT OF THE DISCLOSURE An electric fuse to minimize stresses and strains to which a ribbon-typefusible element is normally subjected on account of thermal expansion and thermal contraction, and for other reasons. The end of minimizing such stresses and strains is achieved by imparting a novel geometry to the ribbon-type fuse link.

Prior state of the art This invention relates to an improvement of the structure disclosed and claimed in US. Patent 3,319,029 to P. C. Jacobs, IL, May 9, 1967, for High-Voltage Fuses Having Zig-Zag-Shaped Fuse Links. Expansion and contraction of zig-zag-shaped fuse links is effected against the restraining forces, or resistance, of the pulverulent arc-quenching medium, or filler, by which the fuse links are surrounded. The smaller these forces, the smaller the wear and tear to which fuse links are subjected by consecutive heating and cooling cycles. The geometry of the fuse link according to the present invention minimizes the damaging action of the pulverulent arc-quenching filler upon the ribbon fuse link. This is particularly important if the packing of the arc-quenching filler is dense. Dense packing of the arc-quenching filler is, in turn, a prerequisite for the best performance of any given fuse design.

Summary of the invention Fuses embodying this invention include a tubular casing of insulating material, terminal elements closing the ends of the casing, and a pulverulent arc-quenching filler inside the casing. Ribbon fuse link means inside the casing conductively interconnect the aforementioned terminal elements. The fuse link means are submersed in the pulverulent arc-quenching filler and they include a pair of axially inner substantially planar sections and a pair of axially outer substantially planar sections integral with said axially inner sections. Each of the pair of said axially inner sections has a point of reduced cross-sectional area and they enclose a predetermined angle, thus defining an edge at the locus of intersection of the planes thereof. Said point of reduced cross-sectional area of each of said pair of axially inner sections is arranged in spaced relation from the aforementioned edge. Each of the aforementioned pair of axially outer sections extends in a direction longitudinally of said casing, each enclosing a predetermined angle with one of said pair of axially inner sections and defining a second edge at the locus of intersection of the plane thereof and the plane defined by one of said pair of axially inner sections. Each of said pair of axially outer sections has a point of reduced cross-sectional area arranged in spaced relation from said second edge.

Brief description of the drawings FIG. 1 is an isometric view of a pair of fuse link means intended for the fuse structure of FIG. 2;

FIG. 2 is a section of a fuse emboding the present invention taken along IIII of FIG. 3;

FIG. 3 is a section along III-III of FIG. 2;

FIG. 4 is a top plan view of a modification of the fuse link means of FIGS. 1 and 2;

FIG. 5 is a side elevation of the fuse link means of FIG. 4;

FIG. 6 shows another fuse embodying this invention and is a section along VIVI of FIG. 7; and

-FIG. 7 shows the same structure as FIG. 6 and is a section along VIIVII of FIG. 6.

Description of preferred embodiments Referring now to the drawings, and more particularly to FIGS. 1, 2 and 3 thereof, reference numeral 1 has been applied to indicate a casing of insulating material which is substantially tubular and closed at the ends thereof by a pair of terminal elements 2. Terminal elements 2 are in the form of metal plugs, plugging the ends of easing l and held in position by transverse steel pins 3 projecting radially through casing 1 into plugs 2. Each plug or terminal element 2 is provided with a knife blade contact 4 integral therewith intended for insertion of the fuse into a fuse holder. Plugs or terminal elements 2 are conductively interconnected by a pair of ribbon fuse link means generally indicated by reference numeral 5. Fuse link means 5 are submersed in a pulverulent arc-quenching filler 6, preferably quartz sand. Each fuse link means 5 includes a pair of axially inner, substantially planar sections 5a each having a point of reduced cross-sectional area 5b. Sections 5a enclose a predetermined angle a and define a first edge 5c at the locus of intersection of the planes thereof. The point of reduced cross-sectional area 512 of each section 5a is arranged in spaced relation from edges 50. Each fuse link means 5 further includes a pair of axially outer, substantially planar sections 5d integral with the aforementioned axially inner sections 5a of ribbon fuse link means 5. Each of the axially outer sections 5d of ribbon fuse link means 5 extends in a direction longitudinally of easing l, and each encloses a predetermined angle [3 with one of the axially inner sections 5a immediately adjacent thereto. Each axially outer section 5b of ribbon fuse link means 5 defines an edge 5e of the locus of intersection of the plane thereof and the plane defined by the axially inner section 5a immediately adjacent thereto. Each axially outer fuse link section 5d has a point of reduced cross-sectional area 5 arranged in spaced relation from the edge 5e immediately adjacent thereto. The axially outer ends of ribbon fuse link means 5 project into grooves 211 provided in the axially inner end surface of terminal plugs 2, and are conductively connected to terminal plugs 2 by solder joints (not shown).

There are two main reasons for causing stresses and strains in ribbon fuse link means 5. One of these reasons are variations of the distance between the axially inner end surfaces of terminal plugs 2, and another of these reasons are variations in the length of ribbon fuse link means 5. Variations of the distance or spacing between the axially inner end surfaces of terminal plugs 2 may be caused by initial manufacturing tolerances, and also by thermal expansion and contraction of the terminal plugs. Variations of the length of ribbon fuse link means 5 are mainly due to thermal expansion and contraction resulting from changes of the current which fuse link means 5 are carrying. Changes or variations of the distance, or spacing, of the axially inner end surfaces of terminal plugs 2 result in a movement of the axially outer sections 5d in a direction longitudinally of casing 1. Such a movement does not result in any significant displacement of the arc-quenching filler, or quartz sand 6, inside of casing 1 and, therefore, such a displacement minimizes the resistance of the arc-quenching filler, or quartz sand, against the movement of sections d. Consequently stresses and strains in sections 5d are minimized. To be more specific, sections 5d are substantially free from any bending stresses, i.e. subjected to tension and compression only. The travel of edges 52 during thermal cycling in a direction longitudinally of casing 1 is relatively small and, as a result, the concomitant travel of edges 50 transversely to casing 1 is quite limited. This, in turn, limits the quantity of arc-quenching filler, or quartz sand, 6 that must be displaced because of the transverse movement of fuse link sections 5a.

The angle a between sections 5a has a significant hearing on the performance of the fuse. This becomes readily apparent when comparing sections 5a and the edge 50 formed between these sections with the bow of a ship, and the arc-quenching filler 6 to be displaced with a body of Water interacting with the ships how. The determination of the angle a between sections 5a is subject to contradictory conditions inasmuch as the displacement of the arc-quenching filler is facilitated by choosing angles a which are less than 90 degrees, and inasmuch as standards of easing sizes and thermal considerations are conducive to selecting angles a substantially exceeding 90 degrees, as shown in FIGS. 1 and 2.

For a better control of the arc-voltage it may be desirable to sandwich portions of fuse link means 5 between plates of insulating material, preferably a laminate of melamine glass cloth, as set forth more in detail in U.S. Patent 2,964,604 to Philip C. Jacobs, In, et al., Current- Limiting Fuses Having Compound Arc-Voltage Generating Means, issued Dec, 13, 1960. In such instances the link-sandwic'hing plates should preferably be arranged on the axially inner fuse sections 5a rather than on the axially outer sections 5d. Such an arrangement of fuselink-sandwiching plates has been shown in FIGS. 4 and 5, wherein reference character 5a has been applied to indicate the axially inner sections of fuse link means 5, reference character 5d has been applied to indicate the axially outer sections of fuse link means 5, and reference character 7 has been applied to indicate pairs of link sandwiching insulating plates enclosing, or covering, the points of reduced cross-sectional area of the axially inner section 5a. The latter are subject to some bending stresses, but significantly stiffened on account of being sandwiched between pairs of insulating plates 7. The axially outer sections 5d do not need to be stiffened since they are substantially free from bending stresses. Plates 7 may be joined by fasteners as, for instance, staples, or eyelets, which is common practice in the fuse art.

Referring now to FIGS. 6 and 7, tubular casing 1 is closed on both ends thereof "by terminal plug 2 held in position by transverse steel pins 3'. Blade cont acts 4' form integral parts of terminal plugs 2'. Each terminal plug 2' is plugged into one of the ends of tubular casing 1' and is provided at the axially inner end surface 2g thereof with a system of radially extending grooves 2h. Plugs 2' are cond'uctively interconnected by a plurality of fuse link means 5. FIGS. 6 and 7 show but three such fuse link means 5'. Actually the structure of FIGS. 6 and 7 is intended to include a number of fuse link means equal to the number of radial grooves in each of the two terminal plugs 2, i.e. eight fuse link means. In the interest of greater clarity but three of these eight fuse link means 5' have been shown in FIGS. 6 and 7. The fuse link means 5 of FIGS. 6 and 7 are substantially the same as the fuse link means 5 of FIGS. 1 and 2 and, therefore, do not need to be described in detail in connection with FIGS. 6 and 7. Sufiice it to state that each fuse link means 5 includes a pair of axially inner sections 5a enclosing a predetermined angle and a pair of axially outer sections 511. The axially outer ends of the axially outer sections 5d of each fuse link means 5' extend into one groove 2h. The axially inner sections 5a of each of the plurality of fuse link means 5 interconnecting plugs 2 are oriented in the same sense,

i.e. they all point in clockwise direction as seen in FIG. 7. Hence the axially inner sections 5a of all fuse link means 5 which are present in the fuse structure push the pulverulent arc-quenching filler 6' in the same sense when the fuse link means 5 expand, or contract. Lengthening of fuse link means 5 results in a slight circular movement of the axially inner portion of the pulverulent arc-quenching filler 6' in clockwise direction, as seen in FIG. 7, and contraction of fuse link means 5' results in a slight circular movement of the axially inner portion of the pulverulent ancquenching filler 6 in counterclockwise direction, as seen in FIG. 7. The work required for effecting this movement is equally shared by each of the several fuse link means 5 of which the structure of FIGS, 6 and 7 is made up. To move the arc-quenching filler 6 requires a predeterminable force and the stress to which each fuse link is subjected is proportional to this force, divided by the number of the fuse link means present. In other words the joint action of the axially inner sections 5a of fuse link means 5' results in a reduction of the stress-es to which each fuse link means 5 is subjected, this reduction being the more significant the larger the number of fuse links involved in the displacement of a portion of the arc-quenching filler 6 in the same sense, or direction.

It is not necessary in order to achieve a sharing between fuse link means of the work involved in displacing the pulverulent arc-quenching filler to stagger the fuse link means in a circular pattern, as shown in FIGS. 6 and 7. The same end may be achieved by staggering all fuse link means in a linear pattern, provided that all axially inner sections are oriented in the same sense, or direction.

It will be understood that I have illustrated and described herein t'wo preferred embodiments of my invention and that various alterations may be made therein without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. An electric fuse comprising:

(a) a tubular casing of insulating material;

(b) terminal elements closing the ends of said casing;

-(c) a pulverulent arc-quenching filler inside said casing; and

(d) ribbon fuse link means inside said casing conductively interconnecting said pair of terminal elements and submersed in said arc-quenching filler, said fuse link means including a pair of axially inner substantially planar sections each having a point of reduced cross-sectional area, said pair of axially inner sections enclosing a predetermined angle and defining a first edge at the locus of intersection of the planes thereof, said point of reduced cross-sectional area of each of said pair of axially inner sections being arranged in spaced relation from said first edge, said fuse link means further including a pair of axially outer substantially planar sections integral with said axially inner sections, each of said pair of axially outer sections extending in a direction longitudinally of said casing and each enclosing a predetermined angle with one of said pair of axially inner sections and defining a second edge at the locus of the intersection of the plane thereof and the plane defined by one of said pair of axially inner sections, and each of said pair of axially outer sections having a point of reduced cross-sectional area arranged in spaced relation from said second edge.

2. An electric fuse as specified in claim 1 including a plurality of fuse link means establishing parallel current paths between said terminal elements, each of said plurality of fuse link means having a pair of axially inner sections pointing in the same sense as the pair of axially inner sections of all the others of said plurality of fuse link means.

3. An electric fuse as specified in claim 1 wherein said terminal elements are formed by a pair of metal plugs plugged into the ends of said casing each having on the axially inner end surface thereof a system of radially ex- 5 6 tending grooves, wherein said pair of metal plugs are con- References Cited ductively interconnected by a plurality of fuse link means UNITED STATES PATENTS establishing parallel current paths between said pair of metal plugs, the axially outer ends of said pair of axially 1,274,119 9/1934 Naher 20O 135 outer sections of each of said plurality of fuse link means 5 264,111 2/1956 Kozacka 200 131 X extending into one of said system of grooves in one of 2,988,620 6/1961 Kozacka 2O0135 X said metal plugs, and the pair of axially inner sections of each of said plurality of fuse link means being oriented in BERNARD GILHEANY Examme" the same sense, H. B. GILSON, Assistant Examiner. 

